Process for the preparation of platinum metal containing aluminosilicates



United States Patent l PROCESS FOR THE PREPARATION OF PLATINUM METALCONTAINING ALUMINOSILICATES Nai Yuen Chen, Cherry Hill, N.J., assignorto Mobil Gil Corporation, a corporation of New York No Drawing.Continuation-impart of application Ser. No. 235,135, Nov. 2, 1962. Thisapplication Apr. 14, 1966,

Ser. No. 542,455

9 Claims. (Cl. 252455) ABSTRACT OF THE DISCLOSURE The invention relatesto a method for preparing crystalline aluminosilicates which contain -ametal of the platinum series. The invention is directed to preparingcrystalline aluminosilicates by incorporating a platinum type metal inthe forming or precursor solutions used for preparing crystallinealuminosilicates, followed by crystallization, washing, drying andcalcining to obtain a crystalline aluminosilicate which contains a metalof the platinum series.

This application is a continuation in part of application Ser. No.235,135 filed Nov. 2, 1962, now forfeited.

This invention relates generally to aluminosilicate catalysts and moreparticularly to a method for preparing aluminosilicates containingtherewithin a metal of the platinum series.

Catalysts containing metals of the platinum series, i.e. metals ofatomic numbers 44 to 46 and 76 to 78 inclusive, have become ofconsiderable commercial significance in recent years. Thus, such metalsimpregnated on alumina and silica-alumina supports are widely employedin reforming operations to produce gasolines of high octane number. Ingeneral, supported platinum metal catalysts are capable of catalyticallyeffecting a variety of complex hydrocarbon conversion reactions. Forexample, it is known that during reforming paraffin hydrocarbons undergoisomerization, naphthenes are dehydrogenated to aromatics and olefinsare hydrogenated to paralfins. In each of these component reactions,however, there is, in so far 'as known, no marked selectivity for anyparticular reactant or group of reactants.

The catalyst of the present invention aifords a platinum groupmetal-containing catalytic composition having the ability to operateselectively on certain members of one or more different reactantsundergoing catalytic conversion. The selectivity attained with the neWcatalysts described herein is believed attributable to the solid,crystalline, zeolitic structure of the support characterized by rigidthree dimensional networks and uniform interstitial dimensions in whichthe platinum metal component is dispersed. By associating the platinummetal in highly dispersed form with the intracrystalline spaces for thechemical reaction system which is to be catalyzed thereby, only suchconversion paths are obtained which involve reactant or productmolecules of such specific shapes or sizes. Such zeolites wherein onlymolecules of particular size and shape are able to enter are sometimesknown as molecular sieves.

Accordingly, it is the primary object of this invention to provide amethod for the preparation of crystalline aluminosilicates which containa metal of the platinum series whereby the crystallinity of thealuminosilicate is substantially unaffected.

It is still another object of this invention to provide a novel processfor the preparation of an aluminosilicate of the aforementioned typewherein the resulting 3,373,119 Patented Mar. 12, 1968 compositionpossesses a high degree of selectivity and activity.

The present invention is based on the discovery that washing, drying andcalcination procedures are critical process steps for obtaining platinummetal-containing crystalline aluminosilicates which have optimumcatalytic selectivity and activity. Various preparational methodsheretofore employed for introducing a metal of the platinum series intothe interstitial channels and cavities of a crystalline aluminosilicatehave been found to effect a loss of crystallinity in the resultingproduct which in turn adversely alfects its molecular shape selectiveproperties. Such preparations usually involve washing thealuminosilicate crystals with water in order to remove the anion portionof the platinum group metal salts. It has now been discovered thatcontinuous washing with Water causes these aluminosilicate catalysts tolose their selectivity since it appears that the crystallinealuminosilicates can transform into the amorphous form, thus releasingthe trapped intracrystalline platinum group metal. It has beendiscovered that the crystallinity of the aluminosilicate can be retainedif the washing solution has a pH of at least 10.0, preferably 10.5 to11.5, and contains a high concentration of the same metallic ions aswere present in the forming solution used to prepare thealuminosilic'ate, i.e. sodium ions if sodium metasilicate and sodiumaluminate were employed. While not wishing to be bound by any theory ofoperation, it nevertheless appears that the aluminosilicate is lesslikely to transform into the amorphous form from the crystalline formWhile in the presence of the above solution. The duration of the washingstep is not narrowly critical since surprisingly it has been found thatthe stability of the aluminosilicate is substantially unaffected by theamount of time it is in contact with the alkaline wash solution.

In preparing the platinum metal-containing aluminosilicates inaccordance with the process of this invention, it has been found that itis necessary to add the salt of the particular metal, for example,tetrammine platinous chloride, directly into the forming solution forthe aluminosilicate rather than base exchanging an already forrnedaluminosilicate with a platinum group metal. While not fullyunderstanding the reasons why, it nevertheless appears that theinclusion of the platinum group metal into the forming solution producesa more uniform product. Therefore, in preparing a platinumaluminosiiicate, for example, according to the instant invention, asolution of sodium aluminate, sodium metasilicate, and a platinum saltare poured simultaneously with stirring into a container maintained at atemperature no higher than about C. with constant stirring untilcrystallization occurs. The particular proportion of the sodiumaluminate and sodium silicate is obviously dependent upon the particularaluminosilicate desired to be synthesized. The mole ratios necessary toprepare a particular aluminosilicate are well known and are described inthe patent literature, e.g., US. Patents 2,882,243; 2,979,381;2,982,612; 2,996,358; 3,008,803, etc.

After formation of the platinum-metal containing aluminosilicate, thealuminosilicate is washed with an alkaline or base solution of 1 to 4normality obtained by the addition of 1 to 4 equivalents of alkali oralkaline earth metal cations to one liter of wash solution, preferablywith a solution having a normality between about 2 and 4, for a periodof time sufficient to remove substantially the mother liquor from thealuminosilicate crystals. The pH of the wash solution is between about10 and 11.5 and is preferably about 10.5. As a further embodiment ofthis invention, small amounts of sodium aluminate and sodiummetasilicate can also be added to the wash solution since theseingredients also aid in maintaining the crystallinity of thealuminosilicate.

Following treatment with the alkaline wash solution, it is thennecessary to rapidly dry the aluminosilicate in air while carefullycontrolling the temperature. The temperature at which the air dryingshould be carried out is below about 140 C. and preferably within therange of 100 to 140 C. A preferred temperature is between about 100 to110 C. The amount of time with which the aluminosilicate is heated atthis temperature is not narrowly critical and is generally no longerthan 40 minutes. A preferred time period ranges from about to minutes.

Immediately after the air drying, it is necessary to calcine thealuminosilicate at a temperature within the range of 350 C. up toslightly below the decomposition temperature of the aluminosilicate inflowing air or other non-absorbing gas. A preferredcalcinationtemperature is between about 380 and 460 C. The duration ofthe calcining step is also not narrowly critical but it has been foundthat about an hour is sufficient in most cases. The particularlypreferred calcination procedureis to heat the aluminosilicate in a thinlayer at about 400 C. for an hour in the presence of flowing air ornon-absorbing gas. While not wishing to be bound by any theory ofoperation, it nevertheless appears that the rapid removal of water fromthe aluminosilicate is extremely necessary in order to maintain itsselectivity and crystallinity. In view of this fact, it is preferredthat both the air drying and calcination step take place in anatmosphere where there is low humidity, e.g., a low partial pressure ofwater, since quite obviously, drying will take place more quickly in aless humid environment.

Although the instant invention has been described with reference to thepreparation of aluminosilicates with a forming solution consisting ofsodium aluminate and sodium metasilicate, it is to be understood thatother forming solutions, conventional in the art, can be employed in theinstant process, such as potassium aluminate, potassium silicate, etc.In this case, the Washing solution would contain potasium ions and havea pH of at least 10.0 and preferably about 10.5.

As still another-embodiment of this invention, it is also possible 'toreplace part or substantially all of the alkali metal cation associatedwith the aluminosilicate with other metallic or non metallic cations. Itis known in the art to contact an aluminosilicate with a solutioncontaining metallic or non metallic cations, e.g., calcium, ammonium,etc., in order to replace part of the original cations with anothercation. This technique can also be employed after crystallization in theprocess of this invention with theexception that the base exchangesolution must have a normality of between about 1 and 4 and a pH of atleast 10.0, preferably about 10.5. In this connection, it is to bepointed out that either the unwashed reaction mixture or the washedplatinum metalcontaining aluminosilicate can be contacted with anydesired cationic solution having the necessary pH. Typical examples ofcations which can be introduced into the aluminosilicate includeammonium, calcium, barium, zinc, nickel, cobalt, and the like.

The method of the present invention may be utilized to incorporateplatinum group metals in a wide variety of crystalline aluminosilicates.The method of the invention is particularly applicable to A-typecrystalline aluminosilicates having a silica to alumina oxide mole ratioof less than 3. Such aluminosilicates include, among others, syntheticcrystalline aluminosilicates identified as zeolites, A, T, ZK-4 andnatural aluminosilicates, such as chabazite.

The amount of platinum group metal introduced into the aluminosilicateforming mixture is generally such that the ultimate crystalline zeolitecontain therein an amount of metal, expressed in terms of metal, fromabout 0.001

percent to about 10 percent by weight, and more usually between about0.001 percent and about 2 percent by weight.

To illustrate the improved crystallinity of the platinummetal-containing aluminosilicate catalysts prepared by the process ofthe instant invention, catalytic oxidation tests were run. These testswere conducted as follows:

A sample of the air dried catalyst of about 0.3 ml. was placed in a 7mm. ID. glass tubular reactor. It was then calcined in a flowing streamof air (10 ml./ min.) for sixty minutes at 400 C. The reactor was cooledto 315 C. in helium (6O ml./min.). A three ml. slug ofhydrocarbon-oxygen-helium' mixture was passed through the reactor andthe reaction products were analyzed on stream by gas chromatography. Thecomposition of the slug was as follows: hydrocarbon (propylene, butaneand isobutane) at 70 mm. Hg partial pressure, oxygen at 530 mm. Hgpartial pressure, helium at 160 mm. Hg partial pressure.

The following examples will illustrate the novel process of thisinvention but it is to be understood that it is not intended to belimited thereto.

Example I A platinum-containing crystalline aluminosilicate of theA-type having a high degree of crystallinity was prepared by admixingthe following solutions:

(A) 92 grams of sodium aluminate (containing 41.3 weight percent A1 0and 35.4 weight percent Na O) and 0.8 gram of tetrammine platinouschloride (Pt(NH Cl dissolved in 400 ml. of distilled water at roomtemperature, filtered and 1 ml. of concentrated ammonium hydroxide addedto the filtrate.

(B) 120 grams of sodium metasilicate (Na SiO -9HO) (containing 21 weightpercent Si0 and 22.9 weight percent Na O) dissolved in 400 m1. ofdistilled water at room temperature.

Solutions A and B are poured simultaneously with stirring into a 1500ml. beaker at room temperature to form a white voluminous and gelatinoussolid.The solid gel is next placed on a water bath and heated withstirring for two hours at about 95 C. with the addition of hot distilledwater to maintain constant solution volume. At the end of two hours, thereaction mixture is heated to a temperature of about to 102 C. andstirring is continued for another three hours.

30 grams of the above crystalline aluminosilicate catalyst containingplatinum were decanted from its mother liquor and then slurried with a100 ml. portion wash solution prepared by dissolving 150 grams of sodiumchloride in 1000 ml. of water. The crystals were then stirred for 15minutes in the wash solution, allowed to stand for 30 minutes and thenfiltered. At this point, the wash procedure was repeated an additionalsix times. A sample of the catalyst was then air dried at C. andcalcined in air at 450 C. at anair flow rate of 10 ml. per minute forone hour and then cooled to 315 C.

The above catalyst was then evaluated for the catalytic oxidation ofnormal butane and isobutane and extensive oxidation of both forms ofbutane (greater than 90%) was observed. The fact that this catalystcatalyzed the oxidation of isobutane demonstrates that its selectivitywas adversely affected.

Example II sodium aluminate, 2.9-grams sodium metasilicate and 2 7 ml.of concentrated ammonium hydroxide in 1000 ml. of water (pH 10.7). Thealuminosilicate was stirred in the wash solution, allowed to stand for30 minutes and then filtered. At this point, the entire washingprocedure was repeated three additional times. The catalyst was then airdried and calcined in the identical manner as in Example I.

When this catalyst was evaluated for catalytic oxidation of apropylene-isobutane mixture, it showed no isobutane combustion, andgreater than 90% oxidation of propylene, clearly demonstrating the factthat it possesses a high degree of crystallinity and selectivity.

Example III The catalyst prepared according to Example II was mixed with100 ml. of calcium acetate solution [prepared by dissolving 176 grams ofcalcium acetate monohydrate in 1000 ml. of water (pH 7.6)], stirred andallowed to stand for 30 minutes. The process Was repeated three timesfollowed by a water wash, after which the catalyst was air dried andcalcined as set forth in Example I. The results of catalytic oxidationindicated combustion of isobutane of 47 percent thereby illustrating thedestruction of crystallinity by a nearly neutral ion exchange solution.

Example IV 30 grams of the crystalline alurninosilicate prepared inExample II were divided into two 15 gram portions. Portion A wasexchanged with an ion exchange solution containing 176 grams calciumacetate monohydrate, 2.5 grams sodium aluminate and 2.9 grams sodiummetasilicate in 1000 ml. water (pH=l0.7). Portion B was exchanged withan ion exchange solution containing 176 grams calcium acetatemonohydrate in 1000 ml. H O (pH=7.6). The exchange procedure was thesame as described in Example III and air drying and calcinationprocedures were the same as in Examle I. Catalytic oxidation testsrevealed that portion A was highly selective (85% n-butane, i-butanecombustion) and portion B was nonselective (50% n-butane, 35% i-butanecombustion). The preservation of crystallinity by an alkaline solutionhaving a pH of 10.7 is clearly demonstrated.

Example V Portion B in Example 4 was divided into two portions. PortionB-l was washed with an ion exchange solution containing 176 gramscalcium acetate monohydrate, 2.5 grams sodium aluminate and 2.9 gramssodium metasilicate in 1000 ml. water. Portion B-Z was washed with anion exchange solution containing 176 grams calcium acetate monohydrateand 1.2 grams sodium hydroxide. Both solutions had a pH of greater than10.0. The exchange procedures were the same as described in Example III.Catalytic oxidation tests revealed that both B-l (79% n-but-ane, 0%i-butane combustion) and B-2 (59% nbutane, 0.4% i-butane combustion)were highly selective. The experiment indicates that alkaline washsolution can not only preserve the crystallinity of the catalyst butalso recover selectivity from a previously non-selective catalyst.

Example VI In Example 4 the samples were air dried and calcined asdescribed in Example I, i.e., calcination was carried out immediatelyafter air drying. In this example, an air dried sample of portion A wasleft exposed in air for 24 hours before the air calcination step wascarried out. Catalytic oxidation tests showed that by exposing the airdried sample to the surrounding atmosphere the sample lost some of itsactivity and selectivity (18% n-butane, 3.3 i-butane combustion).Therefore, the catalyst should be calcined immediately after air dryingin order to preserve selectivity.

Example VII 30 grams of the crystalline alurninosilicate catalystprepared in Example II were kept in its wash solution for 50 days, afterwhich a sample was filtered, air dried and calcined in the same manneras described in Example I. Catalytic oxidation tests indicated more thancombustion of propylene, less than 5% n-butane combustion and 0%i-butane combustion. This demonstrates the stability of the selectivecatalyst in an alkaline medium.

Example VIII Two air dried samples of portion A in Example IV wereplaced in a crucible and calcined in a mufiie furnace at 425 C. and 480C., respectively, and 0.3 gram of each of the calcined samples wereplaced in a micro-reactor. The samples were air treated and tested asdescribed in Example I. Results showed 30% combustion of n-butane and16% combustion of isobutane for 425 C. sample and 8% combustion ofn-butane and 8% combustion of isobutane for the 480 C. sample. Thisdemonstrates that calcination in stagnant (non-flowing air) atmospherelowers the activity and selectivity of the catalyst.

What is claimed is:

1. In a method for the preparation of an alurninosilicate whereby analuminum salt and silicate salt precursor solutions are reacted to forma crystalline aluminosilicate, the improvement which comprisesintroducing a platinum group metal into the reaction mixture prior tocrystallization, washing the resulting crystals with a wash solutionhaving a pH of at least 10.0, drying the resulting crystalline materialat a temperature of less than about 140 C., calcining the resultingproduct at a temperature of at least about 350 C., and thereafterrecovering a crystalline alurninosilicate product in which there iscontained a platinum group metal.

2. The process of claim 1 wherein the washing solution has a pH fromabout 10.5 to 11.5.

3. The process of claim 1 wherein the drying takes place at atemperature of between about to C.

4. In a method for the preparation of an aluminosilicate wherein alkalimetal silicate and an alkali metal aluminate precursor solutions arereacted to form a crystalline alurninosilicate, the improvement whichcomprises introducing a salt of a metal selected from the groupconsisting of platium and palladium into the reaction mixture prior tocrystallization, washing the resulting crystals with a wash solutionhaving a pH of at least 10.0, drying the resulting material at atemperature of less than about 140 C. for a period of time less thanabout 40 minutes, calcining at a temperature of at least 350 C., andthereafter recovering a crystalline alurninosilicate product in whichthere is contained a material selected from the group consisting ofplatinum and palladium.

5. A process for preparing a crystalline alurninosilicate whichcomprises reacting a solution of sodium silicate, sodium aluminate and asalt of a metal selected from the group consisting of platinum andpalladium until crystallization occurs, washing the resulting crystalswith a wash solution having a pH of greater than 10.0, drying thecrystals at a temperature of less than about 140 C., calcining thecrystals at a temperature of at least 350 C. and thereafter recovering acrystalline alurninosilicate product in which there is contained amaterial selected from the group consisting of platinum and palladium.

6. The process of claim 5 wherein the metal salt is a platinum salt.

7. The process of claim 5 wherein the metal salt is a palladium salt.

8. The process of claim 5 wherein the wash solution contains sodiumsilicate and sodium aluminate.

9. A process for preparing a crystalline alurninosilicate whichcomprises reacting sodium aluminate, sodium metasilicate and tetrammineplatinous chloride until crystallization occurs, washing the resultingcrystals with a wash solution having a pH of from 10.5 to 11.5, dryingthe crystals at a temperature of between about 100 C. and 140 C. for aperiod of time of less than 40 minutes, calcining the crystals at atemperature of at least 350 C., and thereafter recovering a crystallinealurninosilicate 7 8 product in which there is contained a materialselected 3,200,083 8/1965 Milton 252-455- from the group consisting ofplatinum and palladium. 1,782,353 ll/ 1930 Iaeger et a1 23-113 X1,840,450 1/1932 Jaeger et a1. 252455 References Cited 2,971,903 2/1961Kimberlin et al. 252-455 UNITED STATES PATENTS 5 3,140,249 7/1964 Planket a1. 252455 2,971,904 2/1961 Gladrow et a1. 252-455 X DANIEL WYMAN,Primary Examiner- 2983570 5/ 1961 Sewbold 252-455 X CARL F. DEES,Assistant Examiner.

